Preheat the oven to 220°C.
Bake potatoes on a bed of salt for 60 minutes.
Preheat the oven to 180°C.
Fry sausages in dripping in a lidded casserole until colored, then remove.
Sauté leeks and onions, then add tomatoes, garlic, herbs, wine, and stock.
Return sausages to the pan and bake covered for 30 minutes.
Remove sausages, discard herbs, and reduce the liquid on the hob until thickened.
Blend the sauce until smooth and pass through a fine sieve.
Fry mushrooms in half the butter and oil, followed by the ham, then drain.
Fry diced bread in remaining butter and oil until golden, then combine with ham and mushrooms.
Scoop baked potato centers and pass through a ricer.
Mix riced potatoes with yolks, apple purée, nutmeg, and seasoning.
Preheat the grill to high and line a tray with baking paper.
Pipe a border of potato onto plates and dry slightly under the grill.
Brush the potato border with egg wash and grill until colored.
Fill the potato border with sausages, top with sauce and mushrooms, then garnish with parsley.